Some strains of chicken are nicer than others. Some breeders cull all their nasty roos and the breeders left are nice. Hence the offspring are nice.

I have had white Orpingtons before from a hatchery. They were almost as aggressive to other chickens as the Golden Sex Links I used to have, and I sold them at auction. My Buff Orpingtons from a hatchery are not nearly as aggressive.

My theory is that they were recently outcrossed with another breed or something- the strain I had.

Don't let me dissuade you from getting white Orps though. You might have a different experience than me.